It’ s a marathon, not a sprint: The management of Impatiens glandulifera at the upper reaches of the river Blees in the Naturpark Our (Luxembourg).

Abstract

The Himalayan balsam (Impatiens glandulifera Royle) is a globally spreading neophyte, which is frequently found along rivers and streams in Luxembourg. To prevent or to fight mass stands of the species, different national management measures along various watercourses are in progress. One of these projects encompasses a 4 km long section located at the upper reaches of the river Blees and its tributaries. Here different control measures were carried out annually during the flowering period of the neophyte since 2017. To evaluate the success of this invasive species management, two surveys were conducted each year, one before (summer – June/July) and one after (autumn – September/October) the removal. Since manual methods (eradication of I. glandulifera by hand) in 2017 were not successful, the management was significantly improved from 2018 onwards using brushcutters for larger and denser populations. In the following years a combination of mechanical and manual measures was used, until mechanical control methods were no longer necessary after 2020. As the number of stands declined, the workload also decreased, to a minimum in 2020 and 2021. This minimal effort was probably insufficient, as there was an obvious increase of I. glandulifera in 2021.We recommend an adapted management of I. glandulifera with a combination of mechanical and manual measures. Which measure is finally used depends not only on the accessibility or the population density of an area, but also on the sensitivity of the occurring biotopes. To ensure a sustainable success of eradication, the measures must be carried out over a long period of time, whereby a certain amount of work must not be undercut. Furthermore, consequential damage to abiotic factors must also be restored after the complete removal of I. glandulifera.